Secondary battery

ABSTRACT

The present disclosure provides a secondary battery, the secondary battery comprises a positive electrode plate, a negative electrode plate, a separator and an electrolyte, the positive electrode plate comprises a positive current collector and a positive film, the positive film is provided on at least one surface of the positive current collector and comprises a positive active material, the negative electrode plate comprises a negative current collector and a negative film, the negative film is provided on at least one surface of the negative current collector and comprises a negative active material, the negative active material comprises graphite, and an average particle diameter of the positive active material represented by D50 and a thickness of the negative film represented by H n  satisfy a relationship: 6≤0.06H n ×(4−1/D50)≤31. The battery of the present disclosure has the characteristics of excellent dynamics performance and long cycle life at the same time.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Chinese patent applicationNo. CN201810442762.5, filed on May 10, 2018, which is incorporatedherein by reference in its entirety.

FIELD OF THE PRESENT DISCLOSURE

The present disclosure relates to the field of battery, and particularlyrelates to a secondary battery.

BACKGROUND OF THE PRESENT DISCLOSURE

Rechargeable batteries are widely used in new energy automotives due tosignificant characteristics of light weight, high energy density, nopollution, none memory effect, long service life and the like. Acharging/discharging process of the rechargeable battery is realized bythe intercalation and the deintercalation of the active ions (such aslithium ions and the like) between the positive active material and thenegative active material, therefore the design of the positive activematerial, the design of the negative active material, the design of thepositive electrode plate and the design of the negative electrode platewill directly affect the performance of the battery. Specifically,whether the positive active material, the negative active material, thepositive electrode plate and the negative electrode plate are reasonablydesigned will affect the charging speed, the energy density, the cycleperformance and the storage performance of the battery.

At present, the common problem existed in the design field of theelectrode plate is that only one certain parameter of the electrodeplate (i.e. the positive electrode plate or the negative electrodeplate) is concerned, such as the per unit area coating weight, thepressing density and the like, however, the improvement on theperformance of the battery is not obvious when only one certainparameter of the electrode plate is improved.

SUMMARY OF THE PRESENT DISCLOSURE

In view of the problem existing in the background, an object of thepresent disclosure is to provide a secondary battery, the battery hasthe characteristics of excellent dynamics performance and long cyclelife at the same time.

In order to achieve the above object, the present disclosure provides asecondary battery, which comprises a positive electrode plate, anegative electrode plate, a separator and an electrolyte, the positiveelectrode plate comprises a positive current collector and a positivefilm, the positive film is provided on at least one surface of thepositive current collector and comprises a positive active material, thenegative electrode plate comprises a negative current collector and anegative film, the negative film is provided on at least one surface ofthe negative current collector and comprises a negative active material.The negative active material comprises graphite, and an average particlediameter of the positive active material represented by D50 and athickness of the negative film represented by H_(n) satisfy arelationship: 6≤0.06H_(n)×(4−1/D50)≤31. A unit of the average particlediameter of the positive active material represented by D50 is μm and aunit of the thickness of the negative film represented by H_(n) is μm.

Compared with the existing technologies, the present disclosure at leastincludes the following beneficial effects: in the present disclosure, byreasonably matching the relationship among the parameters of thepositive active material, the parameters of the negative activematerial, the parameters of the positive negative electrode plate andthe parameters of the negative electrode, the speed of the active ionsdeintercalating from the positive active material and the speed of theactive ions intercalating into the negative active material arereasonably matched, therefore the battery having the characteristics ofexcellent dynamics performance and long cycle life at the same time canbe obtained.

DETAILED DESCRIPTION

Hereinafter a secondary battery according to the present disclosure isdescribed in detail.

The secondary battery of the present disclosure comprises a positiveelectrode plate, a negative electrode plate, a separator and anelectrolyte, the positive electrode plate comprises a positive currentcollector and a positive film, the positive film is provided on at leastone surface of the positive current collector and comprises a positiveactive material, the negative electrode plate comprises a negativecurrent collector and a negative film, the negative film is provided onat least one surface of the negative current collector and comprises anegative active material. The negative active material comprisesgraphite, and an average particle diameter of the positive activematerial represented by D50 and a thickness of the negative filmrepresented by H_(n) satisfy a relationship: 6≤0.06H_(n)×(4−1/D50)≤3 1.A unit of the average particle diameter of the positive active materialrepresented by D50 is μm and a unit of the thickness of the negativefilm represented by H_(n) is μm.

The charging/discharging process of the battery actually is atransferring process of the active ions (such as the lithium ions, thesodium-ions and the like) transferred between the positive activematerial and the negative active material, playing of respectiveperformances of the positive electrode plate and the negative electrodeplate and the reasonable match between the positive electrode plate andthe negative electrode plate both are important parts in the design ofthe battery. The average particle diameter of the positive activematerial is related to the deintercalation speed of the active ions andthe dynamics performance of the positive electrode plate, generally, thesmaller the average particle diameter of the positive active materialis, the faster the deintercalation speed of the active ions is, and thebetter the dynamics performance of the positive electrode plate is. Thethickness of the negative film is related to the intercalation speed ofthe active ions and the polarization degree of the negative electrodeplate, therefore the thickness of the negative film will affect thedynamics performance and the cycle performance of the negative electrodeplate. The active ions are deintercalated from the positive activematerial and then intercalated into the negative active material duringthe charging process of the battery, the matching between the speed ofthe active ions deintercalating from the positive active material andthe speed of the active ions intercalating into the negative activematerial is very important during the charging process of the battery.If the active ions are deintercalated from the positive active materialwith a fast speed, but the negative active material does not have thecapability to timely accept all the active ions, the dynamicsperformance and the cycle performance of the battery will both be worse.

In the design of the battery of the present disclosure, bycomprehensively considering the relationship between the averageparticle diameter of the positive active material represented by D50 andthe thickness of the negative film represented by H_(n) and making themsatisfy a relationship 6≤0.06H_(n)×(4−1/D50)≤31 can make the batteryhave the characteristics of excellent dynamics performance and longcycle life at the same time.

When the average particle diameter of the positive active materialrepresented by D50 is smaller or the thickness of the negative filmrepresented by H_(n) is smaller so as to make a lower limit value of0.06H_(n)×(4−1/D50) be less than 6, the processing process and thepreparation process of the battery become difficult and the energydensity of the battery is very low. When the average particle diameterof the positive active material represented by D50 is larger or thethickness of the negative film represented by H_(n) is larger so as tomake an upper limit value of 0.06H_(n)×(4−1/D50) be more than 31, thethicker negative film affects the intercalation of the active ions,therefore the active ions are easily reduced and precipitated on thenegative electrode plate so as to affect the dynamics performance andthe cycle performance of the battery.

Preferably, the average particle diameter of the positive activematerial represented by D50 and the thickness of the negative filmrepresented by E_(n) satisfy a relationship: 8≤0.06H_(n)×(4−1/D50)≤20.

Furthermore, a morphology of the porous structure of the negative filmwill also affect the dynamics performance of the negative electrodeplate, the developed the porous structure of the negative film is, thestronger the retention capability of the porous negative electrode plateon the electrolyte is, that is the more sufficient the electrolyte inthe porous structure of the negative film is. As thecharging/discharging process of the battery continues, the negativeactive material is repeatedly expanded and contracted, continuous refluxand extrusion of the electrolyte in the porous negative electrode plateis accompanied by during this process; and the more sufficient theelectrolyte in the porous structure of the negative film is, the easierthe reflux and the extrusion of the electrolyte is, the smaller thepolarization during the charging/discharging process of the battery is,and the more beneficial for improving the charging speed of the batteryis. The morphology of the porous structure of the negative film can becharacterized by the pressing density of the negative film, the higherthe pressing density of the negative film is, the more dense the porousstructure of the negative film is, the more difficult the infiltrationof the electrolyte is, the larger the liquid phase conduction resistanceof the active ions inside the porous structure of the negative film is,and the worse the dynamics performance of the negative electrode plateis.

The orientation of the negative film will also affect the dynamicsperformance of the negative electrode plate, generally, when the activeions pass through the SEI membrane on the surface of the negative filmand enter into the negative film, it will be affected by the orientationof the active ion intercalating channels inside the negative film, andthe better the isotropy of the negative film is, the larger the amountof the active ion intercalating channels inside the negative film is,the easier the intercalation process of the active ion is, and thebetter the dynamics performance of the negative electrode plate and thedynamics performance of the battery are. The orientation of all theactive ion intercalating channels inside the negative film can becharacterized by the OI value of the negative film, generally, the OIvalue of the negative film is larger, the active material particles inthe negative film tend to be distributed parallel to the negativecurrent collector, therefore the amount of the active ion intercalatingchannels inside the negative film is smaller, and the dynamicsperformance of the negative electrode plate and the dynamics performanceof the battery are both worse.

In the design of the battery of the present disclosure, bycomprehensively considering the relationship between the pressingdensity of the negative film represented by PD and the OI value of thenegative film represented by V_(OI) and making them satisfy arelationship 0.2≤(PD+0.13×V_(OI))/9.2≤1.3, the dynamics performance andthe cycle performance of the battery can be further improved, and thebattery can bear a larger charging speed. The pressing density of thenegative film represented by PD has a unit of g/cm³.

When the pressing density of the negative film represented by PD islarger or the OI value of the negative film represented by V_(OI) islarger so as to make an upper limit value of (PD+0.13×V_(OI))/9.2 bemore than 1.3, the amount of the active ion intercalating channelsinside the negative film is smaller, the active material particles inthe negative film tend to be distributed parallel to the negativecurrent collector, therefore the dynamics performance of the battery isworse; and moreover, the larger pressing density of the negative filmmakes the porous structure of the negative film more dense, theinfiltration of the electrolyte is more difficult, the liquid phaseconduction resistance of the active ions in the porous structure of thenegative film is larger, therefore the improvement on the dynamicsperformance and the cycle performance of the battery is affected.

When the pressing density of the negative film represented by PD issmaller or the OI value of the negative film represented by V_(OI) issmaller so as to make a lower limit value of (PD+0.13×V_(OI))/9.2 beless than 0.2, the active material particles in the negative film tendto be randomly distributed, the amount of the active ion intercalatingchannels inside the negative film is larger, the porous structure of thenegative film is very developed, and the dynamics performance of thenegative electrode plate is better; however, the electronic conductivityof the negative electrode plate is affected, the charge exchange speedbetween the active ions and the electrons is slower, the negativeelectrode plate also has the risk of exfoliation of the negative filmand wrinkling, therefore the improvement on the dynamics performance andthe cycle performance of the battery is also affected.

Preferably, the pressing density of the negative film represented by PDand the OI value of the negative film represented by V_(OI) satisfy arelationship: 0.3≤(PD+0.13×V_(OI))/9.2≤0.8.

In the secondary battery of the present disclosure, preferably, theaverage particle diameter of the positive active material represented byD50 is 0.5 μm˜15 μm; further preferably, the average particle diameterof the positive active material represented by D50 is 3 μm˜9 μm.

In the secondary battery of the present disclosure, the negative film isprovided on one of the surfaces of the negative current collector or thenegative film is provided on both surfaces of the negative currentcollector. Preferably, the thickness of the negative film represented byH_(n) is 25 μm˜150 μm; further preferably, the thickness of the negativefilm represented by H_(n) is 35 μm˜125 μm. The thickness of the negativefilm represented by H_(n) in the present disclosure refers to thethickness of the negative film on one surface of the negative currentcollector.

In the secondary battery of the present disclosure, preferably, thepressing density of the negative film represented by PD is 0.8 g/cm³˜2.0g/cm³; further preferably, the pressing density of the negative filmrepresented by PD is 1.0 g/cm³˜1.6 g/cm³.

In the secondary battery of the present disclosure, preferably, the OIvalue of the negative film represented by V_(OI) is 1˜150; furtherpreferably, the OI value of the negative film represented by V_(OI) is8˜70.

It should be noted that, an OI value of a powder of the negative activematerial will affect the OI value of the negative film represented byV_(OI) to an extent, therefore the desired OI value of the negative filmrepresented by V_(OI) may be obtained by changing the OI value of thepowder of the negative active material; the OI value of the negativefilm represented by V_(OI) may also be changed by using magnetic fieldinducing technique during the coating process of the negative slurry soas to artificially induce the arrangement of the negative activematerials in the negative electrode plate; the OI value of the negativefilm represented by V_(OI) may also be changed by adjusting the pressingdensity of the negative film during the cold pressing process so as tochange the arrangement of the negative active materials in the negativeelectrode plate.

Preferably, the OI value of the powder of the negative active materialrepresented by G_(OI) is 0.5˜7; further preferably, the OI value of thepowder of the negative active material represented by G_(OI) is 2˜4.5.

In the secondary battery of the present disclosure, the graphite may beone or more selected from a group consisting of artificial graphite andnatural graphite.

In the secondary battery of the present disclosure, the negative activematerial may further comprise one or more selected from a groupconsisting of soft carbon, hard carbon, carbon fiber, mesocarbonmicrobeads, silicon-based material, tin-based material and lithiumtitanate besides the graphite. Preferably, the silicon-based materialmay be elemental silicon, silicon oxide, silicon carbon composite andsilicon alloy; the tin-based material may be elemental tin, tin oxidecompound and tin alloy.

In the secondary battery of the present disclosure, the average particlediameter of the positive active material represented by D50 may beobtained by a laser diffraction particle size analyzer (Mastersizer3000), a volume particle size distribution is obtained according to theparticle size analysis-laser diffraction method (specifically referringto GB/T19077-2016), and the average particle diameter is represented bythe median value D50 in the volume particle size distribution.

The thickness of the negative film represented by H_(n) may be obtainedby an 1/10 micromiter. It should be noted that, the thickness of thenegative film in the present disclosure refers to the thickness of thenegative film of the negative electrode plate after being cold pressedand using for assembling the battery.

The OI value of the negative film represented by V_(OI) may be obtainedby a X-ray powder diffractometer (X'pert PRO), a X-ray diffractionpattern is obtained according to the general rules for X-raydiffractometric analysis JIS K 0131-1996 and the determination method ofartificial graphite lattice parameter JB/T4220-2011, V_(OI)=C₀₀₄/C₁₁₀,C₀₀₄ represents characteristic diffraction peak area of (004) crystalplane, C₁₀₀ represents characteristic diffraction peak area of (110)crystal plane.

The pressing density of the negative film is obtained according to anequation PD=the mass on per unit area negative film (g/cm²)/thethickness of the negative film (cm). The mass on per unit area negativefilm may be obtained by a standard balance, and the thickness of thenegative film may be obtained by a 1/10 micrometer.

In the secondary battery of the present disclosure, the negative filmfurther comprises a conductive agent and a binder, the types and thecontents of the conductive agent and the binder are not specificallylimited and may be selected based on actual demands. The type of thenegative current collector is not specifically limited and may beselected based on actual demands, and preferably, the negative currentcollector is a copper foil.

In the secondary battery of the present disclosure, the positive filmfurther comprises a conductive agent and a binder, the types and thecontents of the conductive agent and the binder are not specificallylimited and may be selected based on actual demands. The type of thepositive current collector is not specifically limited and may beselected based on actual demands, and preferably, the positive currentcollector is an aluminum foil.

It should be noted that, the secondary battery of the present disclosuremay be a lithium-ion battery or a sodium-ion battery.

Specifically, when the secondary battery is the lithium-ion battery, thepositive active material may be selected from lithium cobalt oxide,lithium nickel oxide, lithium manganese oxide, lithium nickel manganeseoxide, lithium nickel cobalt manganese oxide, lithium nickel cobaltaluminum oxide and olivine-type lithium-containing phosphate, but thepresent disclosure is not limited to these materials, otherconventionally known materials that can be used as the positive activematerial of the lithium-ion battery can also be used. These positiveactive materials may be used alone or may be used two or more of them incombination. Preferably, the positive active material may be one or moreselected from a group consisting of LiCoO₂, LiNiO₂, LiMnO₂, LiMn₂O₄,LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ (NCM333), LiNi_(0.5)Co0.2Mn_(0.3)O₂(NCM523), LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ (NCM622),LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂ (NCM811), LiNi_(0.85)Co_(0.15)Al_(0.05)O₂,LiFePO₄ and LiMnPO₄.

Specifically, when the secondary battery is the sodium-ion battery, thepositive active material may be selected from transition metal oxideNa_(x)MO₂ (M represents transition metal, preferably, M is one or moreselected from a group consisting of Mn, Fe, Ni, Co, V, Cu and Cr,0<x≤1), polyanion-type material (phosphate-type, fluorophosphate-type,pyrophosphate-type and sulfate-type) and prussian blue material, but thepresent disclosure is not limited to these materials, otherconventionally known materials that can be used as the positive activematerial of the sodium-ion battery can also be used. These positiveactive materials may be used alone or may be used two or more of them incombination. Preferably, the positive active material may be one or moreselected from a group consisting of NaFeO₂, NaCoO₂, NaCrO₂, NaMnO₂,NaNiO₂, NaNi_(1/2)Ti_(1/2)O₂, NaNi_(1/2)Mn_(1/2)O₂,Na_(2/3)Fe_(1/3)Mn_(2/3)O₂, NaNi_(1/3)Co_(1/3)Mn_(1/3)O₂, NaFePO₄,NaMnPO₄, NaCoPO₄, prussian blue material and a material with a generalformula of A_(a)M_(b)(PO₄)_(c)O_(x)Y_(3-x) (A is one or more selectedfrom a group consisting of H⁺, Li⁺, Na⁺, K⁺ and NH₄ ⁻; M representstransition metal cation, preferably, M is one or more selected from agroup consisting of V, Ti, Mn, Fe, Co, Ni, Cu and Zn; Y represents anionof halogen, preferably, Y is one or more selected from a groupconsisting of F, Cl and Br; 0<a≤4, 0<b≤2, 1≤c≤3, 0≤x≤2).

In the secondary battery of the present disclosure, the specific typeand the specific composition of the separator and the electrolyte arenot specifically limited and may be selected based on actual demands.

Hereinafter the present disclosure will be described in detail incombination with examples. It should be noted that, the examplesdescribed in the present disclosure are only used for explaining thepresent disclosure, and are not intended to limit the presentdisclosure.

Batteries of examples 1-41 and comparative examples 1-6 were allprepared in accordance with the following preparation method.

(1) Preparation of a Positive Electrode Plate

NCM523 (positive active material), acetylene black (conductive agent)and PVDF (binder) according to a mass ratio of 96:2:2 were uniformlymixed with NMP (solvent), which then became homogeneous under stirringvia a vacuum mixer, a positive slurry was obtained; then the positiveslurry was uniformly coated on both surfaces of aluminum foil (positivecurrent collector), drying was then performed under room temperature andcontinual drying was performed in an oven, which was then followed bycold pressing and plate cutting, finally the positive electrode platewas obtained.

(2) Preparation of a Negative Electrode Plate

Graphite or a mixer of graphite and other active materials with acertain mass ratio (negative active material), acetylene black(conductive agent), CMC (thickening agent) and SBR (binder) according toa mass ratio of 96.4:1:1.2:1.4 were uniformly mixed with deionized water(solvent), which then became homogeneous under stirring via a vacuummixer, a negative slurry was obtained; then the negative slurry wasuniformly coated on both surfaces of copper foil (negative currentcollector), drying was then performed under room temperature andcontinual drying was performed in an oven, which was then followed bycold pressing and plate cutting, finally the negative electrode platewas obtained.

(3) Preparation of an Electrolyte

Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethylcarbonate (DEC) according to a volume ratio of 1:1:1 were mixed togetherto obtain an organic solvent, then sufficiently dried LiPF₆ (lithiumsalt) was dissolved into the mixed organic solvent to obtain anelectrolyte, and a concentration of the electrolyte was 1 mol/L.

(4) Preparation of a Separator

The separator was a polyethylene membrane.

(5) Preparation of a Lithium-Ion Battery

The positive electrode plate, the separator and the negative electrodeplate were laminated in order, the separator was positioned between thepositive electrode plate and the negative electrode plate so as toseparate the positive electrode plate from the negative electrode plate,then the positive electrode plate, the separator and the negativeelectrode plate were wound together to form an electrode assembly, thenthe electrode assembly was put into a case, which was followed bybaking, electrolyte injection, vacuum packaging, standby, formation,shaping and the like, finally a lithium-ion battery was obtained.

Hereinafter test processes of the lithium-ion batteries were described.

(1) Testing of the Dynamics Performance:

At 25° C., the lithium-ion batteries prepared in the examples and thecomparative examples were fully charged at a constant current of 4 C andfully discharged at a constant current of 1 C for 10 cycles, then thelithium-ion batteries were fully charged at a constant current of 4 C,then the negative electrode plates were disassembled from thelithium-ion batteries, and the lithium precipitation on the surface ofeach negative electrode plate was observed. The lithium-precipitationarea of less than 5% was considered to be slight lithium precipitation,the lithium-precipitation area of 5% to 40% was considered to bemoderate lithium precipitation, and the lithium-precipitation area ofmore than 40% was considered to be serious lithium precipitation.

(2) Testing of the Cycle Performance:

At 25° C., the lithium-ion batteries prepared in the examples and thecomparative examples were charged at a constant current of 3 C anddischarged at a constant current of 1 C, the fully charging/dischargingcycle process was repeated until the capacity of the lithium-ion batterydecayed to 80% of the initial capacity, and the cycle number of thelithium-ion battery was recorded.

TABLE 1 Parameters and test results of examples 1-41 and comparativeexamples 1-6 D50 of positive active Negative film (PD + Negativematerial Active H_(n) PD 0.06H_(n) × 0.13 × lithium Cycle (μm) material(μm) (g/cm³) V_(OI) (4 − 1/D50) V_(OI))/9.2 precipitation number Example1 7.2 graphite 26 1.40 20.0 6.0 0.43 slight 2865 lithium precipitationExample 2 7.2 graphite 35 1.40 20.0 8.1 0.43 no lithium 3458precipitation Example 3 7.2 graphite 42 1.40 20.0 9.7 0.43 no lithium3963 precipitation Example 4 7.2 graphite 54 1.40 20.0 12.5 0.43 nolithium 3543 precipitation Example 5 7.2 graphite 62 1.40 20.0 14.4 0.43no lithium 2988 precipitation Example 6 7.2 graphite 84 1.40 20.0 19.50.43 no lithium 2875 precipitation Example 7 7.2 graphite 112 1.40 20.025.9 0.43 slight 1765 lithium precipitation Example 8 7.2 graphite 1321.40 20.0 30.6 0.43 slight 1431 lithium precipitation Example 9 4.7graphite 39 1.03 4.0 8.9 0.17 slight 1856 lithium precipitation Example10 4.7 graphite 39 1.05 8.0 8.9 0.23 slight 2311 lithium precipitationExample 11 4.7 graphite 39 1.17 12.0 8.9 0.30 no lithium 2452precipitation Example 12 4.7 graphite 39 1.25 22.0 8.9 0.45 no lithium3100 precipitation Example 13 4.7 graphite 39 1.40 31.0 8.9 0.59 nolithium 3121 precipitation Example 14 4.7 graphite 39 1.52 42.0 8.9 0.76no lithium 2976 precipitation Example 15 4.7 graphite 39 1.60 54.0 8.90.94 no lithium 2851 precipitation Example 16 4.7 graphite 39 1.58 68.08.9 1.13 slight 2198 lithium precipitation Example 17 4.7 graphite 391.59 75.0 8.9 1.23 slight 2410 lithium precipitation Example 18 4.7graphite 39 1.60 82.0 8.9 1.33 moderate 1345 lithium precipitationExample 19 3.4 graphite 65 1.05 9.6 14.5 0.25 no lithium 2340precipitation Example 20 4.5 graphite 67 1.09 13.6 15.2 0.31 no lithium3654 precipitation Example 21 5.3 graphite 71 1.17 20.7 16.2 0.42 nolithium 2280 precipitation Example 22 7.2 graphite 73 1.21 26.8 16.90.51 no lithium 3455 precipitation Example 23 4.3 graphite 76 1.22 31.717.2 0.58 no lithium 3057 precipitation Example 24 4.7 graphite 77 1.2535.0 17.5 0.63 no lithium 4028 precipitation Example 25 5.2 graphite 801.32 37.3 18.3 0.67 no lithium 2877 precipitation Example 26 5.7graphite 82 1.38 42.5 18.8 0.75 no lithium 3219 precipitation Example 277.2 graphite 84 1.40 47.3 19.5 0.82 no lithium 2122 precipitationExample 28 6.4 graphite 89 1.52 54.1 20.5 0.93 slight 1879 lithiumprecipitation Example 29 8.5 graphite 92 1.55 60.3 21.4 1.02 slight 2003lithium precipitation Example 30 6.5 graphite 99 1.56 68.0 22.8 1.13slight 1786 lithium precipitation Example 31 7.3 graphite 102 1.58 76.323.6 1.25 slight 1567 lithium precipitation Example 32 1.1 graphite 821.42 10.6 15.2 0.30 no lithium 2314 precipitation Example 33 2.3graphite 91 1.38 14.5 19.5 0.35 no lithium 2534 precipitation Example 3411.2 graphite 67 1.65 24.3 15.7 0.52 no lithium 2134 precipitationExample 35 13.4 graphite 82 1.56 15.8 19.3 0.39 no lithium 2011precipitation Example 36 14.2 graphite 74 1.32 16.4 17.4 0.38 no lithium2876 precipitation Example 37 20.2 graphite 68 1.65 32.1 16.1 0.63 nolithium 2098 precipitation Example 38 0.5 graphite 161 1.65 32.1 19.30.63 no lithium 2309 precipitation Example 39 4.3 graphite + soft 771.23 16.7 17.4 0.37 no lithium 2407 carbon (7:3) precipitation Example40 7.6 graphite + hard 67 1.15 16.0 15.6 0.35 no lithium 2497 carbon(7:3) precipitation Example 41 5.3 graphite + lithium 74 1.78 7.2 16.90.30 no lithium 2309 titanate (7:3) precipitation Comparative 0.4graphite 61 1.40 20.0 5.5 0.43 moderate 598 example 1 lithiumprecipitation Comparative 25 graphite 135 1.40 20.0 32.1 0.43 slight 906example 2 lithium precipitation Comparative 4.1 graphite 160 1.40 20.036.1 0.43 moderate 756 example 3 lithium precipitation Comparative 13.2graphite 20 1.40 20.0 4.7 0.43 serious 453 example 4 lithiumprecipitation Comparative 9 graphite 135 1.40 20.0 31.5 0.43 serious 234example 5 lithium precipitation Comparative 1.1 graphite 30 1.40 20.05.6 0.43 serious 397 example 6 lithium precipitation

It could be seen from the test results of Table 1, the batteries ofexamples 1-41 had the characteristics of excellent dynamics performanceand long cycle life, this was because the positive active material, thenegative active material, the positive electrode plate and the negativeelectrode plate had a good matching relationship, the speed of thelithium ions deintercalating from the positive active material and thespeed of the lithium ions intercalating into the negative activematerial were reasonably matched, the demands of the battery on a alarge rate and a fast speed could be met, therefore the battery mighthave excellent dynamics performance and the battery might also have longcycle life while charged under a large rate and a fast speed.

Examples 1-8 illustrated the test results where the average particlediameter of the positive active material represented by D50 was constantas 7.2 μm, when the thickness of the negative film represented by H_(n)was adjusted to make the value of 0.06H_(n)×(4−1/D50) be between 6 and31, the battery might have the characteristics of excellent dynamicsperformance and long cycle life at the same time. Preferably, the value0.06H_(n)×(4−1/D50) was between 8 and 20.

When the average particle diameter of the positive active materialrepresented by D50 was smaller or the thickness of the negative filmrepresented by H_(n) was samller so as to make the lower limit value of0.06H_(n)×(4−1/D50) be less than 6, the capacity performance of thebattery while charged under a large rate and a fast speed was worse, thedynamics performance of the battery was worse, and the energy density ofthe battery was also very low. When the average particle diameter of thepositive active material represented by D50 was larger or the thicknessof the negative film represented by H_(n) was larger so as to make theupper limit value of 0.06H_(n)×(4−1/D50) be more than 31, the thickernegative film affected the intercalation of the lithium ions, thereforethe lithium ions were easily reduced and precipitated on the negativeelectrode plate, which would also affect the dynamics performance andthe cycle performance of the battery.

The preferred range of the average particle diameter of the positiveactive material represented by D50 was 0.5 μm˜15 μm, the preferred rangeof the thickness of the negative film represented by H_(n) was 25 μm˜150μm. And what the applicant needed to explain was, when one or two of theaverage particle diameter of the positive active material represented byD50 and the thickness of the negative film represented by H_(n) did notfall within the above preferred ranges, but the value of0.06H_(n)×(4−1/D50) was between 6 and 31, the battery might still havethe characteristics of excellent dynamics performance and long cyclelife at the same time. For example, in example 37 and example 38, theaverage particle diameter of the positive active material represented byD50 and the thickness of the negative film represented by H_(n) both didnot fall within the above preferred ranges, but by reasonably adjustingthe relationship between the average particle diameter of the positiveactive material represented by D50 and the thickness of the negativefilm represented by H_(n) and making the value of 0.06H_(n)×(4−1/D50) bebetween 6 and 31, the speed of the lithium ions deintercalating from thepositive active material and the speed of the lithium ions intercalatinginto the negative active material might be reasonably matched, and thebattery might still have the characteristics of excellent dynamicsperformance and long cycle life at the same time. When the averageparticle diameter of the positive active material represented by D50 andthe thickness of the negative film represented by H_(n) both fell withinthe above preferred ranges, but the value of 0.06H_(n)×(4−1/D50) was notbetween 6 and 31, the dynamics performance and the cycle performance ofthe battery were both worse. The thickness of the negative filmrepresented by H_(n) was too larger compared to the average particlediameter of the positive active material represented by D50 incomparative example 5, the intercalation of the lithium ions wasseriously affected, serious lithium precipitation occurred on thenegative electrode plate, and the dynamics performance and the cycleperformance of the battery were both worse. The thickness of thenegative film represented by H_(n) and the average particle diameter ofthe positive active material represented by D50 in comparative example 6were both very small, the lithium ions could deintercalate from thepositive active material with a fast speed, however, the thinnernegative film did not have the capability to timely accept all thelithium ions deintercalating from the positive active material, part ofthe lithium ions would be reduced and precipitated on the surface of thenegative electrode plate, serious lithium precipitation occurred on thenegative electrode plate, and the dynamics performance and the cycleperformance of the battery were both worse.

Examples 9-18 further adjusted the relationship between the pressingdensity of the negative film represented by PD and the OI value of thenegative film represented by V_(OI), and when they satisfied arelationship 0.2≤(PD+0.13 ×V_(OI))/9.2≤1.3, the dynamics performance andthe cycle performance of the battery could be further improved.

When the pressing density of the negative film represented by PD and theOI value of the negative film represented by V_(OI) were unreasonablydesigned and the upper limit value of (PD+0.13 ×V_(OI))/9.2 was morethan 1.3, the larger OI value of the negative film made the negativeactive material particles tend to be distributed parallel to thenegative current collector, the amount of the lithium ion intercalatingchannels inside the negative film was smaller, and the dynamicsperformance of the negative electrode plate was worse; and moreover, thelarger pressing density of the negative film made the porous structureof the negative film more dense, the infiltration of the electrolyte wasmore difficult, the liquid phase conduction resistance of the lithiumions in the porous structure of the negative film was larger, thedynamics performance of the negative electrode plate was furtherdeteriorated, therefore the improvement on the dynamics performance andthe cycle performance of the battery was affected. When the pressingdensity of the negative film represented by PD and the OI value of thenegative film represented by V_(OI) were unreasonably designed and thelower limit value of (PD+0.13 ×V_(OI))/9.2 was less than 0.2, thesmaller OI value of the negative film made the negative active materialparticles tend to be randomly distributed, the amount of the lithium ionintercalating channels inside the negative film was larger, the porousstructure of the negative film was very developed, the dynamicsperformance of the negative electrode plate was better; however, theelectronic conductivity of the negative electrode plate was affected,the charge exchange speed between the lithium ions and the electrons wasslower, therefore the improvement on the dynamics performance and thecycle performance of the battery was also affected. The dynamicsperformance and the cycle performance of the batteries prepared inexample 9 and example 18 were slightly worse than that of the batteriesprepared in examples 10-17.

What is claimed:
 1. A secondary battery comprising a positive electrodeplate, a negative electrode plate, a separator and an electrolyte, thepositive electrode plate comprising a positive current collector and apositive film, the positive film being provided on at least one surfaceof the positive current collector and comprising a positive activematerial, the negative electrode plate comprising a negative currentcollector and a negative film, the negative film being provided on atleast one surface of the negative current collector and comprising anegative active material; wherein the negative active material comprisesgraphite, and an average particle diameter of the positive activematerial represented by D50 and a thickness of the negative filmrepresented by H_(n) satisfy a relationship: 6≤0.06H_(n)×(4−1/D50)≤31; aunit of the average particle diameter of the positive active materialrepresented by D50 is μm, a unit of the thickness of the negative filmrepresented by H_(n) is μm.
 2. The secondary battery according to claim1, wherein 8≤0.06H_(n)×(4−1/D50)≤20.
 3. The secondary battery accordingto claim 1, wherein the average particle diameter of the positive activematerial represented by D50 is 0.5 μm˜15 μm.
 4. The secondary batteryaccording to claim 3, wherein the average particle diameter of thepositive active material represented by D50 is 3 μm˜9 μm.
 5. Thesecondary battery according to claim 1, wherein the thickness of thenegative film represented by H_(n) is 25 μm˜150 μm.
 6. The secondarybattery according to claim 5, wherein the thickness of the negative filmrepresented by H_(n) is 35 μm˜125 μm.
 7. The secondary battery accordingto claim 1, wherein a pressing density of the negative film representedby PD and an OI value of the negative film represented by V_(OI) satisfya relationship: 0.2≤(PD+0.13×V_(OI))/9.2≤1.3, and a unit of the pressingdensity of the negative film represented by PD is g/cm³.
 8. Thesecondary battery according to claim 7, wherein0.3≤(PD+0.13×V_(OI))/9.2≤0.8.
 9. The secondary battery according toclaim 7, wherein the pressing density of the negative film representedby PD is 0.8 g/cm³˜2.0 g/cm³.
 10. The secondary battery according toclaim 9, wherein the pressing density of the negative film representedby PD is 1.0 g/cm³˜1.6 g/cm³.
 11. The secondary battery according toclaim 7, wherein the OI value of the negative film represented by V_(OI)is 1˜150.
 12. The secondary battery according to claim 11, wherein theOI value of the negative film represented by V_(OI) is 8˜70.
 13. Thesecondary battery according to claim 1, wherein an OI value of a powderof the negative active material represented by G_(OI) is 0.5˜7.
 14. Thesecondary battery according to claim 13, wherein the OI value of thepowder of the negative active material represented by G_(OI) is 2˜4.5.15. The secondary battery according to claim 1, wherein the negativeactive material further comprises one or more selected from a groupconsisting of soft carbon, hard carbon, carbon fiber, mesocarbonmicrobeads, silicon-based material, tin-based material and lithiumtitanate.